The present invention relates to optically clear articles comprising delicate surface films, e.g., thin organic or inorganic films which function as light filters, polarizers or the like. Specifically, the invention is concerned with an optically clear article comprising a thin delicate surface film, wherein at least part of the surface film is provided with a plastic coating which protects the film from the damaging effects of scratching, moisture and abrasion.
Laminated articles comprising a combination of glass and plastic laminae are well known in the art. U.S. Pat. No. 3,781,184 to Domicone et al., for example, discloses glass-plastic laminated windshields comprising an inner layer of soft polyvinyl butyral which is protected from abrasion by a polyvinyl fluoride film. U.S. Pat. No. 3,808,077 to Rieser et al., discloses glass-plastic laminated articles for vehicle windshields comprising polyvinyl acetal or polyurethane layers which may optionally be protected with thin plastic films.
In the ophthalmic field, many attempts to combine the desirable properties of glasses and plastics are found in the patent literature. German Auslegeschrift No. 1,284,588 describes photochromic composites comprising photochromic glass and plastic layers, while German Gebrauchsmuster No. 1,985,755 discloses glass-glass composites for ophthalmic lenses which comprise a polarizing film interlayer.
As noted in the prior art, a major problem relating to glass articles comprising an exposed delicate film, composed for example of a soft organic material such as plastic, is that of protecting the delicate film from damage due to scratching or moisture. By a delicate film is meant an organic or inorganic film exhibiting low resistance to damage from scratching, abrasion, or moisture. Examples include polymeric plastic films such as polyvinyl butyral, polyvinyl alcohol, or polyvinyl chloride, inorganic photochromic films such as silver halide layers, and also organic or inorganic dye layers deposited alone or in combination with temporary or permanent organic underlayers or carrier films.
In the field of protective coatings, a great deal of attention has been directed to the development of coating compositions which may be applied to glass articles such as glass containers, to protect them from scratching damage (which can impair strength), or to glass lenses to impart properties such as fogging resistance or the like thereto. Hence, Netherlands Patent Application No. 72.16492 describes acrylic-melamine-silane coatings for glass lenses or the like which protect against surface condensation, while German Patent Application No. 2,732,062 discloses two-layer protective coatings such as polyester/acrylic coatings, for protecting glass bottles from damage.
The problem of protecting delicate films from scratching and moisture damage is quite different from that of protecting glass containers from such damage. In the former instance, the protective coating must be disposed on a delicate base, rather than a hard inert inorganic base, a factor which can increase the vulnerability of the coating to damage by scratching point loads. Also, the protective coating must exhibit good bonding and chemical compatibility with the delicate film itself, rather than with a glass surface, and must exhibit a high degree of moisture resistance, optical clarity, smoothness and weatherability. Finally, the coating must be inexpensive and relatively simple to apply.
Hard or brittle coatings which offer good abrasion resistance on hard plastic or glass substrates may not be suitable for use in protecting delicate films of the kind above described. Hence, amino resin coatings such as melamine coatings, or coatings composed of silicates or vacuum-deposited silica, are too brittle for use on soft organic films and crack easily under scratching point loads. Such coatings can also crack in the event of swelling of the underlying film, which can occur in the presence of moisture. On the other hand, many of the softer coatings (e.g. polyurethane or silicone coatings) which can effectively protect glass containers from scratching damage, are readily torn by point loads when disposed as thin (e.g. not exceeding about 2 mils in thickness) layers on soft organic underlayers.
It is therefore a principal object of the present invention to provide a transparent, optically clear article comprising a delicate organic or inorganic surface film wherein the film is protected from moisture, scratching and abrasion damage by a thin protective plastic coating as hereinafter described.
It is a further object of the present invention to provide an optically clear glass article comprising a light-polarizing surface film wherein the light polarizing surface film is protected from moisture, scratching or abrasion damage by a thin protective plastic coating as hereinafter described.
It is a further object of the invention to provide an optically clear glass article comprising a light-polarizing surface film which is suitable for use as an ophthalmic lens, wherein the surface film is protected by a thin protective plastic coating and wherein the glass is a photochromic glass which reversibly darkens on exposure to light.
Other objects and advantages of the invention will become apparent from the following description thereof.